table cache lease too short cause load data infinitely

[tiancaiamao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Testing table cache feature, sysbench oltp_read_only, table size 100000, 32 tables, 'alter table cache'
When the machine load is heavy, load table takes more than 3s
However, the default lease time is 3s...
It means the loaded data is outdated immediately, so the date is reloaded, and the process repeat forever

It waste a lot of CPU resource and make the QPS low.

2. What did you expect to see? (Required)

Table cache lease is long, and load data is fast, so the load data is infrequent and renew lease enlarge the TTL of the loaded data.

3. What did you see instead (Required)

Table cache lease is short, and load data takes long.
The data is outdated immediately after it's loaded! So the loading process repeat again and again

4. What is your TiDB version? (Required)

master 2ae7132

[tiancaiamao]

It can be work around by set the @@tidb_table_cache_lease to a larger value, for example, set it to 10 and the problem disappear.